Icebreaker

ABSTRACT

For improving the headway and sternway icebreaking characteristics, the hull of a ship has the greatest width of the icebreaking waterline in the forebody and has trimming and ballasting in the stern area, whose part located above the icebreaking waterline is widened to such an extent that on lowering the afterbody by trimming or ballasting during sternway travel, a channel is broken in the ice cover, which is wider than the wide forebody part passing through said channel during sternway travel.

This is a continuation of co-pending application Ser. No. 149,132 filed on Jan. 27, 1988 and now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an icebreaker with the maximum icebreaking waterline width in its forebody and with trimming and ballasting means.

It is known that icebreacking ships can more effectively break ice the further forward is displaced the widest part of the icebreaking waterline in the headway direction. This improvement is reversed in the case of sternway movement.

For certain icebreakers with special tasks, such as e.g. convoy icebreakers, significance is not only attached to the capacity of effectively being able to break ice when making headway, but also the capacity to rapidly change the direction of travel and also to be able to break a fixed ice cover in the case of sternway travel.

EP-A-No. 0070002 discloses a ship for travelling in open or ice-covered water with a pontoon-like forebody located above the waterline, which has parallel side walls and an end face extending over the entire breadth of the ship and which under water is planar and markedly forwardly inclined, which towards the stern passes into a centre keel, whilst also having an afterbody having drive means housed therein, in which the lateral edges in the transition region of the forebody side walls to the end face are curved in the longitudinal direction of the lateral edges and project in such a way sideways with respect to the planes formed by the forebody side walls, that the distance between the lateral edges located under the construction line forms the maximum underwater hull width. The undersides of the frames between the two lateral edges from the point of the ship's length at which the end face passes into the centre kneel, to the point at which it reaches the ship's bottom are constructed athwartships downwardly curved or bent. In the case of a ship constructed in this way more favourable conditions are provided for shear fracture of a one-part floe from the fixed ice cover and the guidance of the floe beneath the water is improved, with a reduce risk of crushing the floe into small fragments, so that it is possible to even more reliably ensure that the floe is brought under the fixed ice cover.

If in the case of an icebreaker constructed in this way headway travel takes place on the normal icebreaking waterline and sternway travel on the trimmed waterline, the following situation arises. In the case of headway, two lateral cutting edges provided on the prow produce a smoothly cut, ice-free fracture channel in the ice cover and regularly shaped, approximately rectangular ice floes are moved laterally beneath the unbroken ice cover and are removed from the region of the propeller. In the case of sternway travel, e.g. through the laterally projecting cutting edges located on the bow and forming the widest part of the hull, a fracture channel is produced in the ice, in that the broken ice is raised to the sides in the same way as by a snow plough. In this case, it is neither possible to prevent ice contact with the propeller, nor the entry of broken ice into the channel.

SUMMARY OF THE INVENTION

The problem of the present invention is to provide an icebreaker which is particularly suitable for sternway icebreaking and for icebreaking when turning a circle, in which the optimum headway and sternway icebreaking characteristics are combined.

According to the invention this problem is solved by so constructing an icebreaker of the aforementioned type that the part of the stern of the hull located above the icebreaking waterline is widened in such a way that on lowering the afterbody by trimming or ballasting the ship during sternway travel, a channel is broken in the ice cover, which is wider that the wide forebody part passing through this channel during sternway travel.

It has been found that in the case of an icebreaker constructed in this way optimum headway and sternway icebreaking characteristics are combined, which is brought about in that the shape of the afterbody is such that on lowering thereof by trimming or ballasting the ship, there is a clearly widened waterline in the afterbody. According to a further embodiment of the invention the widening of the above-water hull is such that on increasing the draught of the stern and headway in turning circle, the projecting length of the afterbody initiates a second icebreaking process towards the outside of the turning circle fracture channel, which widens the channel and reduces the turning circle diameter. It is particularly advantageous that, whilst the bow produces in uniform manner approximately rectangular ice floes, the breaking shoulder provided on the afterbody initiates a further breaking process widening the channel and reducing the turning circle and through which smaller ice floes are produced, which are largely passed laterally beneath the unbroken ice cover together with the ice floes broken by the forebody. In addition, with a ship constructed in this way, there is no need to in energy-consuming manner raise ice out of the water during sternway travel.

Further appropriate developments of the invention can be gathered from the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show:

FIG. 1--A side view of an icebreaker with the normal icebreaking waterline, trimmed icebreaking waterline and lowered icebreaking waterline.

FIG. 2--Views from above of waterlines of known icebreakers with different forebody shapes for increasing improvement of the icebreaking capacity.

FIG. 3--A side view of a known icebreaker with normal icebreaking waterline and trimmed icebreaking waterline..

FIG 4--A plan view of the icebreaker according to FIG. 3 during a headway travel on the normal icebreaking waterline.

FIG. 5--A plan view of the icebreaker according to FIG. 3 in the case of sternway travel on the trimmed waterline.

FIG. 6--A plan view of an icebreaker for headway turning circle travel in the ice with breaking shoulders provided laterally in the afterbody region.

FIG. 7--A view from above of a rudder rotor located inthe propeller way.

FIG. 8--A plan view of FIG. 6 hull showing schematically a ballast tank and pumping system for increasing selectively the draught of the stern and/or the bow of the hull.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings 1 is the normal waterline, 2 the direction of travel of an icebreaker 100, 3a the lowered icebreaking waterline, 3 the trimmed icebreaking waterline for an icebreaker with breaking shoulders 5 positioned laterally on the afterbody and 6 the ice floes produced by said shoulders 5. The icebreaker 100 comprises the hull 10, whose forebody is 11, afterbody 12 and bow 13.

FIG. 1 in conjunction with FIG. 2 shows the increasing improvement of the icebreaking capacity from waterline form A as the poorest form, via waterline form B, to waterline form C as the best form of known hull configurations. Relative to the aforementioned known icebreakers, FIGS. 3 to 5 show the icebreaking process in the case of forward travel (FIG. 4) on the normal icebreaking waterline 1 and during rearward travel (FIG. 5) on the trimmed icebreaking waterline 3, it being clearly visible that a smooth cut ice-free breaking channel is formed in the ice cover during forward travel, regularly shaped, approximately rectangular ice floes 4 being passed laterally beneath the unbroken ice cover and removed from the vicinity of the ship's propeller. During rearward travel with the stern lowered on waterline 3 a breaking channel is produced in the ice, permitting the passage of the cutting edges on the bow and forming the widest part of the bow in the broken channel.

The disadvantages occuring in the known icebreakers are avoided in the case of an icebreaker 100 according to FIG. 6. As is shown in FIG. 6, the afterbody 12 of hull 10 of icebreaker 100 is provided with breaking shoulders 5, constructed on either side of the hull 10 in the afterbody region. The largest breaking channel width B1 obtained through breaking shoulders 5 is larger than the largest forebody width B, so that in the case of a trimmed afterbody 12, the breaking shoulders or the particular breaking shoulder initiates a more extensive breaking process widening the breaking channel and reducing the turning circle. The ice floes are indicated at 6.

The afterbody configuration is roughly as shown in FIG. 6. The afterbody 12 can be wider than the forebody 11. In the case of the embodiments shown in FIG. 6, the waterline regions 14, 15 in the afterbody area 12 pass into laterally projecting, i.e. widening sections 5a, so that the waterlines of the afterbody 12 have a roughly lobar widening, but the afterbody design can also differ from that shown in FIG. 6. Thus, e.g. the transitions of the ship sides 14, 15 in the vicinities of sections 5a can be linear to the partially elliptical profile 5b, but it is considered advantageous for flow reasons to provide arcuate sections 5a, which have a sliding surface-like action.

The construction of the afterbody 12 of an icebreaker 100 shown in FIG. 6 is particularly favourable for headway turning circle travel in the ice.

The means necessary for trimming and ballasting the hull 10 are constructed to permit selectively increasing the draught of the bow or the stern of the hull as suggested in FIG. 8. Increasing the draught of the stern of the hull 10 for improving the sternway icebreaking characteristics is brought about by rapidly pumping round ballast water in the longitudinal direction of the ship or by taking additional ballast water. To improve the lateral icebreaking process through the stern, it is advantageous to use high-performance rudders.

FIG. 7 shows a high-performance rudder arranged in the wash of a propeller 9, which improves the icebreaking action of the breaking shoulders 5 at the stern of hull 10. It is preferable to use rudders which are not sensitive to ice contact, such as a rotor rudder 7 with an integrated rotary-driven cylinder 8 enabling, in known manner, transverse forces of 50 to 65% of the forward thrust of the main propeller to be produced.

The icebreaker with the greatest width of the icebreaking waterline 1 formed in the forebody and with trimming and ballasting means, is constructed like that the part of the stern 12 of the hull 10 located above the icebreaking waterline 1. The stern afterbody 12 is widened in such a way that on lowering the afterbody 12 by trimming or ballasting the ship during sternway travel, a channel is broken in the ice cover, which is wider than the wide forebody part 11 passing through this channel during sternway travel. The widening of the above-water hull 10 is such that on increasing the draught of the stern 12 and headway in turning circle, the projecting length of the afterbody 12 initiates a second icebreaking process towards the outside of the turning circle fracture channel, which widens the channel and reduces the turning circle diameter.

The draught of the stern 12 can be increased for improving the sternway icebreaking characteristics by rapidly pumping round ballast water in the longitudinal direction of the hull or by taking on additional ballast. For this purpose of improving the lateral icebreaking process through the stern 12 high-performance rudders 7, 8 are provided, which for example, may be constructed as rotor rudders.

In the vicinity of the afterbody 12 of the hull 10 breaking shoulders 5 are provided on either side at which in the vicinity of its breaking shoulders, the afterbody 12 of the hull 10 may have a greater width than the forebody. 

What is claimed is:
 1. An icebreaker for performing icebreaking both in headway and sternway travel, said icebreaker having a hull with the width of the icebreaking hull greater in the forebody than in the hull midsection, and with trimming and ballasting means, an afterbody part of the stern of the hull located above the hull waterline, said afterbody being widened in such a way that on lowering the afterbody by trimming or ballasting the ship during sternway travel a channel is broken in the ice cover which is wider than a channel formed solely by the wide forebody part passing through this channel during sternway travel.
 2. An icebreaker according to claim 1, wherein said widened afterbody includes shoulder portions projecting beyond said hull midsection such that on increasing the draught of the stern while turning and while travelling forwardly, the projecting shoulder portions of the afterbody initiate a second icebreaking process towards the outside of the turning circle fracture channel, which widens the channel and reduces the turning circle diameter.
 3. An icebreaker according to claim 2, wherein the draught of the stern can be increased for improving the sternway icebreaking characteristics by rapidly pumping round ballast water in the longitudinal direction of the hull or by taking on additional ballast.
 4. An icebreaker according to claim 3, wherein for improving the lateral icebreaking process through stern, high-performance rudders are provided.
 5. An icebreaker according to claim 4, wherein rotor rudders are used as the high-performance rudders.
 6. An icebreaker according to claim 5, wherein in the vicinity of the afterbody of the hull breaking shoulders are provided on either side.
 7. An icebreaker according to claim 6, wherein in the vicinity of its breaking shoulders, the afterbody of the hull has a greater width than the forebody.
 8. An icebreaker boat hull having a forebody, a midsection, and an afterbody, said hull having a normal water line defining a horizontal plane when the boat is not under power, trimming and ballasting means in the hull to alter said normal water line relative to the actual water line to increase the draught of the hull forebody during forward hull movement, said trimming and ballasting means also increasing the draught of the hull afterbody-during sternwise travel of the boat, said hull forebody so shaped that the hull forebody has a wider beam above said normal water line, said hull afterbody so shaped that the hull afterbody has a wider beam above said normal water line, and said hull midsection having a beam less than that of said forebody and less than that of said after body, and shoulder portions of said afterbody adjacent said hull midsection.
 9. The icebreaker hull construction of claim 8 wherein the hull afterbody has a maximum width at least as great as that of the maximum width of the hull forebody. 